Siloxane-modified polyolefin elastomers are under development for use in the manufacture of power cable accessories, e.g., cable joints, splices, separable connectors, cable termination, etc., by injection molding. These new polymers offer the possibility of injecting thick parts in a thermoplastic mode, de-molding the part, and storing it for latent cure off-mold under ambient conditions, i.e., without the need for external moisture or heat. This approach has the potential of substantially cutting the manufacturing cycle time for making these parts.
This new technology is a two-component system comprising (1) a polyolefin containing silane functionality in combination with a hydroxy-terminated silicone polymer, or a blend of a vinyl silane, polyolefin, peroxide and a hydroxy-terminated silicone polymer, and (2) a catalyst masterbatch, i.e., a catalyst carried in a suitable base polymer. These components need to be adequately blended with one another in a melt mixing operation prior to the injection step to ensure efficient and uniform crosslinking.
One potential challenge for the implementation of this technology is that the current injection molding manufacturing process relies on rubber injection molding equipment in which the material is first roll-milled and then shaped into a strip, i.e., tape, for feeding into an extruder mounted on the molding machine. These machines are typically fitted with rubber extruders which are designed for simple masticating and pressurization. These extruders are typically short in length, and thus have limited, if any, mixing capability.
Accordingly, a need exists for a method by which the reactive base compound and catalyst masterbatch are delivered to the injection molding machine without equipment modification and with minimum interaction between the two components prior to feeding to the molding machine so as to avoid premature reaction (scorch) of the components in the melt.